Hot Wire Cutter

F

fritz42_male

Senior Member
Hey guys, I fancy building myself a hot wire cutter for polystyrene. December Silicon Chip magazine has an article on this but using a 555 timer for PWM and an IRF540. I fancy doing this with an 08M and IRL540 - got the bits already. Anybody see any issues?

What's the simplest way of powering an 08M from 12V regulated supply? - I was thinking a 5V Zener with current limiting resistor as per the article.
 
E

eclectic

Moderator
fritz42_male said:
Hey guys, I fancy building myself a hot wire cutter for polystyrene. December Silicon Chip magazine has an article on this but using a 555 timer for PWM and an IRF540. I fancy doing this with an 08M and IRL540 - got the bits already. Anybody see any issues?

What's the simplest way of powering an 08M from 12V regulated supply? - I was thinking a 5V Zener with current limiting resistor as per the article.
Click to expand...
Not a clue if this is of any help, but,
http://www.picaxeforum.co.uk/showthread.php?t=6095&highlight=wire+cutter

e
 
J

Jaguarjoe

Senior Member
Michael 2727 said:
To get a little extra Oomph out of the IRF540 I ran the Picaxe
at around 5.6V to 5.7V via a zener from memory.
Click to expand...
Why did you use an IR-F-540 instead of the logic level IR-L-540? Prolly wouldn't have needed to run the 'axe at a higher voltage then. The 2k2 and 47k voltage divider hurts gate drive too. Prolly could have used ~100R instead of 2K2. It's only needed to prevent gate ringing.
 
S

SAborn

Senior Member
I made a few quick and dirty hot wire foam cutters some years back that worked rather well with no need for tricky circuits.

The basic system consists of a 2 amp transformer 12 or 24 volt with a standard 240 volt household light globe in series with the active mains wire to the transformer.
The light bulb limits the power that the transformer can draw and prevents it from burning out

The low voltage side of the transformer is connected as a dead short via the hot wire, (i used 0.6mm mig welding wire)

Changing the wattage of the light bulb adjusts the temperature of the wire.
On one wire cutter i added a light dimmer to the light bulb circuit for extra temperature adjustment
 
R

Rbeckett

Member
fritz42_male said:
Hey guys, I fancy building myself a hot wire cutter for polystyrene. December Silicon Chip magazine has an article on this but using a 555 timer for PWM and an IRF540. I fancy doing this with an 08M and IRL540 - got the bits already. Anybody see any issues?

What's the simplest way of powering an 08M from 12V regulated supply? - I was thinking a 5V Zener with current limiting resistor as per the article.
Click to expand...
If you are using the wire cutter for wing blanks we tend to use a pot on a variable amp/volt PS and adjust as high as possilble without damaging the wing core. Nichrome resistance wire and hard plastic blanks on either end and off ya go. It is then possible to meld 2 or even 3 different airfoil contours over the length of the wing. Add a vacuum bagged thin sheeted skin and they are tough as nails for very cheap. We even use the blue insulation board from the big box stores to get in excess of 16 foot wing spans on high lift gliders for University engineering projects. Lots of fun on a high start with a 10 LB droppable weight.
Bob
 
F

fritz42_male

Senior Member
Thanks for the replies. I'm about to go ahead with one of those cheap 2A hard disk power supplies off eBay - 12V for the hotwire and 5V for the Picaxe. If this doesn't have enough grunt, I have a 12V 5A supply instead however, I want to keep the cost down to a minimum - does anybody see an issue with powering the picaxe via a zener and resistor?

It's just for general foam cutting not wing blanks. I'm hoping to keep the total cost under US$20 for a competition.
Trouble is the US$ has slumped. lol
 
M

MartinM57

Moderator
fritz42_male said:
I want to keep the cost down to a minimum - does anybody see an issue with powering the picaxe via a zener and resistor
Click to expand...
Depends on what the PICAXE is doing aka how much current it is sourcing (or sinking, if the power for the load is also taken from the same point)

Do the sums - an nice exercise in simple circuit theory ;). Say the initial "power supply" is...
Code: 
12v -> 680R -
              |
          5v1 zener
              |
            GND
..and then imagine the PICAXE being connected and you want it to source say 20ma into a LED. So the PICAXE is a bit like a 5V/0.02A resistor = 250R placed at that junction point and going to ground.

So now re-analyse the circuit with a 250R resistor from the junction of the 680R and the Zener to ground. What's the voltage (and hence the power supply to the PICAXE) at that point now?
 
Last edited:
J

Jeremy Leach

Senior Member
Hi RBeckett, are there any photos online about your 16 foot wingspan gliders? I used to be into RC gliders and that sounds impressive/interesting ! 100in Wingspan was the biggest I made though :eek:
 
M

Michael 2727

Senior Member
Hi JaguarJoe,
At the time I had some IRF450s and no logic level ones,
which are common as dirt these days.

I didn't need the full rated current (33A) available and
at 4.5v the data sheet says they should deliver around 10A,
the extra 1 volt input doubles that figure.

IRF540s are almost as cheap as lollies/candy and easy to source.
Sometimes you just use what you have on hand, and if it works all the better ~ ;o)
 
W

westaust55

Moderator
fritz42_male said:
Hey guys, I fancy building myself a hot wire cutter for polystyrene. December Silicon Chip magazine has an article on this but using a 555 timer for PWM and an IRF540. I fancy doing this with an 08M and IRL540 - got the bits already. Anybody see any issues?

What's the simplest way of powering an 08M from 12V regulated supply? - I was thinking a 5V Zener with current limiting resistor as per the article.
Click to expand...
Keep in mind that not everyone knows where to look for the referenced project.

Here are the SiChip mag links to two hot wire cutter projects:

April 2000 version:
http://www.siliconchip.com.au/cms/A_102846/article.html
schematic
http://www.siliconchip.com.au/cms/gallery/article.html?a=102846&i=13

and the Dec 2010 version:
http://www.siliconchip.com.au/cms/A_112248/article.html
currently cannot get to the schematic to check out the potential for PICAXE-ability

EDIT: short time later got into the right page for the schematic:
http://www.siliconchip.com.au/cms/gallery/article.html?a=112248&i=10

EDIT2: the 555 have a fairly broad voltage rage up to about 15V from memory whereas the 08M will not survive long at much over 5.5V.
IMHO consider a more stable regulator - a 100mA LDO type could be suitable for the 08M alone.
 
Last edited:
F

fritz42_male

Senior Member
westaust55 said:
EDIT2: the 555 have a fairly broad voltage rage up to about 15V from memory whereas the 08M will not survive long at much over 5.5V.
IMHO consider a more stable regulator - a 100mA LDO type could be suitable for the 08M alone.
Click to expand...
Thanks - what do you suggest for the LDO? a Zener and resistor will cost about 20c and I am REALLY counting the pennies on this one to try and keep within the competition rules.

63c for an IRL540, 58c for a 10K pot, $5 for the nichrome wire, $5 for the 08M, a bit of Vero and a plastic case from my bits box for about $3 and about $3.60 for a hard disk power supply off eBay.

Getting close to $20 and I haven't budgeted for the wood, bolts and spring yet!
 
W

westaust55

Moderator
Missed the earlier comment about a $20 cost limitation.

Maybe you will have to stay with the resistor and zener. But maybe gof for a 4.5 or 4.8V zener and test the circuit at low current to check the voltage.

An LP2940S-5 is a 5V 100 mA LDO regulator is $1.16 from Futurlec
Since your supply is in fact relatively high even a 78L05 regulator (5V 100 mA) would do at $0.21ea from Futurlec.

If you already had purchased a handful or were purchasing other bits for the future to almost eliminate the postage cost (typical total is AUD$4-00) on a per component basis, then the 78L05 would have been an ecomonical and better option.
 
J

Jaguarjoe

Senior Member
You might be able to use Guitar string wire. I've read that "high e" 0.25mm wire is a lot less expensive than nichrome wire.
 
S

SAborn

Senior Member
Piano wire works well to, if you can get your paws on some.

As i said above mig welding wire (0.6mm) works well also.

Just remember to make it so the wire is able to coil up underneath so when it gets burnt and stretched or it breaks you can just feed some more through and terminate it at the top.
 
F

fritz42_male

Senior Member
Thanks very much guys for all the suggestions. I have 7805 in my bits box as well as Nichrome wire. Seeing as the cost is so close to a zener and resistor, I'll probably go that way if the hard disk PSU doesn't have enough grunt and I have to go with the higher current 12V only PSU.

I'll price up a guitar string and already have MIG wirebut Perth is bloody expensive on stuff like this - however I bought the Nichrome off Dick Smith before they discontinued such stuff and it only cost $3.50 so I'll probably argue for that or find a US supplier (this is a mainly US forum that I'm entering the competition in).

Quite fun having such a small amount of money to play with!
 
Last edited:
M

Michael 2727

Senior Member
Standard 0.6mm MIG wire will only last a short while, if it is Stainless Steel MIG wire
well that's a different story, but last quote I got was around $350.00/spool AUD.
Nichrome or Stainless wire does not oxidize much when heated, hence it lasts 10x longer.

The old style Jug/Kettle Elements work well and are cheap, but rare these days.
Bunnings or M10 may have them Radio Parts used to, not now I think.

You take the Jug coil off the ceramic holder, thread the coil onto some thick
wire then draw it out into a single length. Watch it does not take off near
the end or you'll get a Birds Nest. < $5.00 AUD used to buy you one.

EDIT: BTW @ 0.6mm you need a TON of current to drive it HOT, pre-red.

You could always rat the wire out of an old cheapy AC Fan Heater, for that matter
a brand new one, prolly cheaper than E-bay wire + Postage ~ ;o)
 
Last edited:
S

SAborn

Senior Member
The whole point with using mig was was its cheap and has strength to it.

The factor that is often overlooked is you need a wire with some rigidity as once its hot it stretches and snaps easy.

From my experience you don't want a glowing red hot wire as this melts the foam around the wire rather than a clean cut, as you do corners etc the feed rate slows down and if the wire is too hot it melts big gouges out of the foam.

I use 0.6mm steel mig wire with a 2 amp transformer at 24v.

Different metals used in different wire types have different resistances so the heat of the wire will vary between wire types.
 
F

fritz42_male

Senior Member
SAborn said:
The whole point with using mig was was its cheap and has strength to it.

The factor that is often overlooked is you need a wire with some rigidity as once its hot it stretches and snaps easy.

From my experience you don't want a glowing red hot wire as this melts the foam around the wire rather than a clean cut, as you do corners etc the feed rate slows down and if the wire is too hot it melts big gouges out of the foam.

I use 0.6mm steel mig wire with a 2 amp transformer at 24v.

Different metals used in different wire types have different resistances so the heat of the wire will vary between wire types.
Click to expand...
Good point. I have 2 different types of 'heating' wire - Nichrome and can't remember what the other one is and I have MIG wire and am picking up an 'E' string. So will try the 2A supply first with all wire types and then grade up if I have to.
 
You must log in or register to reply here.
Top